In a related method of forming a carbon nanotube (CNT), a metal, for example, a transition metal such as Fe, Co, Ni or many others, is deposited on a solid substrate (typically Alumina or anodic aluminum oxide (AAO)). Heat is applied to break the metal film into a plurality of catalyst particles. In a chemical vapor deposition reactor operating at an appropriate temperature, pressure and gas composition, a carbon containing gas such as ethylene, or other hydrocarbon gas drifts over the catalyst particles and some molecules deposit onto their surface. Carbon containing species diffuse and decompose within the catalyst particle to ultimately crystallize into CNTs which grow out of the catalyst particles.
In another related method, a porous substrate is provided. This substrate may be formed by exposing an aluminum substrate to an acid treatment in an electrolytic bath, thereby forming the pores. These pores have one opening, and are solid on the bottom. Intermetallic catalyst particles are deposited electrolytically at the bottom of the pores. Gas is passed over the substrate, as described above, and the CNTs grow within the pores.
Wetting is not a desired property in these methods. Instead, lack of wetting is necessary in order to favor the beading of a thin catalyst film into small nanospheres during a thermal treatment process (in a Hydrogen/Helium atmosphere) which is crucial for CNT growth.
During gas phase CVD growth, when two nanotubes touch each other, there will be a driving force trying to increase their contact surface, ultimately forcing the CNTs to adhere to one another. The catalyst engine will stall when the catalyst particle of one of the CNTs touches and immerses in the other CNT.